The goal of this research is to understand how the cerebellum aids eye movements. We know that the cerebellum is important in every movement we make, but we do not know exactly what it does or how it does it. We can make progress faster by investigating the cerebellum with eye movements than with limb or other movements because we know much more about how the brain produces eye movements than any other movements. Our results will also help us understand how the brain produces eye movements. Eye movements are an important part of our lives. Every day we make tens of thousands of eye movements to look at things of interest and see them clearly. Abnormalities in eye movements severely reduce our ability to read, see, and visually guide our other movements. Among other projects, we are investigating the role of the cerebellum in the ability to make eye movements accurate after something has made them inaccurate. The cerebellum has been implicated in the unconscious lear ning that keeps our movements accurate, but we do not know what role it plays. In 1998 we published a description of the way in which making many repeated rapid eye movements affects the performance of these movements. This will help us correctly interpret data on eye movement adaptation that we collect from monkeys. We also published two abstracts. One describes the role of a particular part of the cerebellum, the posterior interpositus nucleus, in smooth eye movements. The cerebellum is critical for these smooth movements. This work will tell us what this part of the cerebellum contributes. The other abstract describes a difference between two kinds of rapid eye movements. The cerebellum contributes a different influence to these two kinds of movements. The difference between them tells us about cerebellar function. FUNDING NIH grants EY00745 and EY10578 and by the Deutsche Foschungsgemeinschaft (Heisenberg-Program Str 436/1-1). *Straube, A., Robinson , F.R., and Fuchs, A.F. Decrease in saccadic performance after many visually guided saccadic eye movements in monkeys. Invest. Ophthal. 38 2810-2816, 1998. *Robinson, F.R., and Brettler, S.C. Smooth pursuit properties of neurons in the ventrolateral posterior interpositus nucleus of the monkey cerebellum. Soc. Neurosci. Abstr. 24 1405, 1998. Eggert, T., Mezger, F., Robinson, F.R., and Straube, A. Position dependency of gain is different in visually and memory guided saccades. Soc. Neurosci. Abstr. 24 670, 1998.